It is known that fuel cell stacks produce electrical energy directly via an electrochemical redox reaction using hydrogen (the fuel) and oxygen (the oxidant) without passing via a mechanical energy conversion step. This technology seems promising, especially for motor vehicle applications. A fuel cell stack comprises in general the series combination of unitary elements each consisting essentially of an anode and a cathode separated by a polymeric membrane allowing ions to pass from the anode to the cathode.
It is very important to have a precise evaluation of the sealing state of the fuel cell, that is to say the sealing of the gas circuit at the anode (fuel gas circuit) and the sealing of the oxidant gas circuit (gas circuit at the cathode). This is because a gas leak will inevitably disturb the operation of the fuel cell stack and pollute the environment thereof, in particular if this is a fuel gas leak. As a consequence, the fuel cell stack may suffer a loss of power, a reduction in efficiency or premature ageing, and the operating conditions, for safe operation, may even be compromised.
Patent application WO 2003/061046 discloses an extinction procedure for a polymer electrolyte membrane fuel cell operating with air as oxidant gas. The procedure disclosed consists in maintaining the pressure difference between the anode and the cathode below an acceptable level. To do so, the air feed is maintained during extinction and the air pressure is controlled so as to follow the drop in pressure on the hydrogen side. However, maintaining the air feed risks causing a hydrogen starvation, which for stack survival is quite worrying. Moreover, the above document teaches no means for observing the sealing state of a fuel cell stack.